1. Field of the Invention
The present invention relates to an endosteal implant assembly and more particularly, to a novel abutment/anchor, hereinafter referred to as anchor, for adjustably supporting one or more prosthetic teeth or appliances at a desirable orientation relative to the path of insertion of the restoration. The present invention is particularly suited, but not limited, to use with patient-removable restorations.
2. Background of the Prior Invention
A dental prosthesis for replacing one or more missing teeth may be accomplished by placement of one or more dental implants in the jawbone and corresponding number of anchors to which the dental prosthesis is secured thereto. The anchor is normally screwed or bonded into the implant. The implant is generally made from a titanium alloy or other rigid materials which are non-reactive with human tissue or fluid.
It is well known that the angle of a dental anchor must be aligned with the intended angle of the path of insertion of the restoration and must be maintained from abutment to abutment, in cases where multiple implants are employed, to facilitate a smooth and non-traumatic insertion and function of a removable or a fixed appliance. The determination of the most desirable path of insertion of the appliance may be governed by factors such as the position of adjacent natural teeth, arc of closure, ridge contour and the patient's dexterity. Prior inventions for adjustably aligning the prosthetic tooth are disclosed, for example, in U.S. Pat. No. 4,713,004 to Linkow et al, U.S. Pat. No. 4,738,623 to Driskell, U.S. Pat. No. 4,780,080 to Haris, U.S. Pat. No. 4,832,601 to Linden, U.S. Pat. No. 4,854,872 to Detsch, U.S. Pat. No. 4,907,969 to Ward, U.S. Pat. No. 4,932,868 to Linkow et al, and U.S. Pat. No. 4,934,935 to Edwards.
Specifically, it is well known in the present field to place a dental implant in the jawbone, whereby through the process of osseointegration the bone grows closely around the implant, permanently integrating the implant into the jawbone. Various attempts have been made in the past to properly align the dental anchor in relation to the path of insertion with an improperly aligned dental implant so that a prosthetic tooth, which is to be formed on the dental anchor, properly aligns with the neighboring teeth. One example of the prior technique is disclosed in U.S. Pat. No. 4,713,004 to Linkow et al (Linkow). In this example, an implant is placed in the bone and one end of an angled threaded shaft is threaded into the implant and rotated into a proper orientation. A wedge shaped collar having an angled upper surface is placed around the angled shaft and the upper surface is positioned to coincide with the angle of the shaft so that the free end of the shaft extends perpendicularly from the angled surface. A prosthetic tooth anchor is threaded on the free end of the shaft to secure the collar in a set orientation. Linkow also discloses an alternative embodiment of aligning a prosthetic tooth, in which, instead of the angled shaft and collar, an intermediary anchor having a ball and socket joint is threaded in the implant. A bolt, which is attached to a prosthetic tooth anchor, is screwed completely through the ball to fix the position of the ball relative to the socket once an alignment has been accomplished.
Another technique employed in the prior art is disclosed in U.S. Pat. No. 4,780,080 to Haris. Haris places a conventional dental implant in the jawbone, and also secures an intermediary anchor to the implant. To correct the improper orientation of the implant and the anchor, an asymmetrically shaped frusto-conical prosthetic tooth anchor is positioned coextensively with the intermediary anchor. By rotating the asymmetrically shaped anchor about the longitudinal axis of the implant, various alignments can be achieved. Once a proper setting is identified, the frusto-conically shaped anchor is bonded to the intermediary anchor while the intermediary anchor is still permanently secured to the implant.
Yet another technique employed in prior art is disclosed in U.S. Pat. No. 4,832,601 to Linden. Linden utilizes a hexagonally-shaped intermediary anchor which is fastened to a complementary hexagonal bore formed in a dental implant. A prosthetic tooth anchor is adjustably secured to the intermediary anchor with a screw. The intermediary and the prosthetic tooth anchors function much like a ball and socket joint when the screw is loosened. That is, the prosthetic tooth anchor may move universally within the intermediary anchor. Once a proper alignment is made, the intermediary anchor and the prosthetic anchor may then be entirely removed from the implant. The screw is then tightened to immobilize the prosthetic support anchor relative to the intermediary anchor. The prosthetic support anchor with a prosthetic tooth formed thereon and the intermediary anchor is then placed back into the implant and secured thereto by a conventional means such as bonding or by a mechanical means.
Finally, U.S. Pat. No. 4,934,935 to Edwards also employs a conventional implant technique for setting an implant in the jawbone. An intermediary anchor is temporarily plugged into the implant and is properly positioned therein by rotating the anchor which is set at a predetermined angle. The anchor is then bonded to the implant once properly positioned. A prosthetic tooth anchor is then screwed into the angled intermediary anchor for supporting a prosthetic tooth thereon.
While these prior inventions make provisions for aligning a prosthetic tooth with the neighboring teeth, there are numerous disadvantages. These would include extreme complexity, to a point of impossible execution in actual clinical situations; limited application, suited only to fixed, permanently cemented restorations such as bridges or single crowns; not applicable to patient-removable restorations; the necessity of screw access holes on the chewing surfaces of the artificial teeth (described as "Swiss Cheese" effect in recent literature); and limited serviceability and retrievability of abutments or anchors. In short, the prior inventions do not present a simple, practical method for independent alignment of implant supported retrievable anchors for patient-removable restorations.